It is known in the art for hydraulic dampers to include a main piston assembly in a main section of a tube of the damper, and a secondary piston assembly in a narrowed section of the tube. The secondary piston assembly forms a so called hydraulic stop arrangement that generates additional damping force over a predefined end section of an operating range of piston rod travel. Exemplary dampers provided with such a hydraulic stop arrangements are disclosed in U.S. Pat. No. 3,447,644 and European Patent Application Pub. Nos. EP 2 302 252A2 and EP 2 952 775A2.
Such hydraulic stop arrangements enable the generation of an additional damping force depending mainly on the position of the piston rod and provide a progressive increase of damping force based on rod displacement. The increase of a damping force in such solutions may, in certain cases, be excessively abrupt. Accordingly, it has been proposed to provide the secondary piston assembly with an additional compression valve assembly that makes the additional damping force generated by a stop arrangement dependent also on the rod speed.
An exemplary damper of this type is described in U.S. Patent Appln. Pub. No. US 2011/017558 which discloses a hydraulic compression stop piston that includes a main element having ducts, a flow limiting disc spring covering the ducts, and working in the motion of the compression piston, a flow limiter that covers the ducts with the expansion, stop washers, and limiting parts.
Nonetheless, all such known hydraulic stops feature the progressive characteristic of the additional damping force in the whole operating range of a stop. Although such a progressive characteristic is advantageous, it also generates a high risk of generating excessive damping forces which may induce extremely high loads to various damper components (in particular components of the hydraulic stop arrangement itself) and other structural vehicle components which may be damaged.
In view of the foregoing, it is an object of the present invention to provide a hydraulic damper with a hydraulic stop arrangement that provides a high and progressive increase of damping force based on rod displacement while also limiting an increase of damping forces above a certain tunable threshold. It is another object of the invention that the damper is of a simple construction, cost efficient and simple to manufacture.